The technique of structuring a network in a home area by the power line communication (PLC: Power Line Communication) is already in practical use. Such power line communication makes it possible to establish communication between PLC modems (power line communication devices) each connected to an outlet, in which a power line (domestic wiring) is used as a signal transmission path. Accordingly, without the necessity of laying a dedicated communication cable in the home area, a wired LAN (local area network) can be structured (for example, see Non Patent Literature 1). To each PLC modem, an appliance having an information communication function, such as a personal computer, is connected via a communication line. Further, not being limited to the personal computer, it is also possible to connect a household electrical appliance, which has added functions of receiving external control and providing information externally, to the PLC modem, so as to be included in the network (for example, see Patent Literature 1).
However, it is troublesome to purchase and install a PLC modem per household electrical appliance. Also, it is inconvenient that the PLC modem occupies one outlet. Further, there is a case where installation of the PLC modem is physically difficult, such as on a wall surface or the like. Accordingly, it is preferable that a household electrical appliance previously includes a PLC modem, from the viewpoint of functionality and of promoting the prevalence of the PLC.
FIG. 5 is a diagram showing a circuit configuration example of a case where a PLC modem is installed in a household electrical appliance. With reference to the drawing, household electrical appliance 63 often includes power supply circuit 62 for supplying a DC power supply voltage to an electronic circuit which is installed for a control purpose. Power supply circuit 62 converts a commercial AC voltage supplied via plug 63p into a prescribed DC voltage. PLC modem 61 is connected in parallel on the primary side of power supply circuit 62, and is connected to power line 65 by plug 63p being inserted into outlet 64.
PLC modem 61 is structured with PLC modem circuit unit 611, high frequency transformer 612 for coupling with the power line, and capacitors 613. Further, PLC modem circuit unit 611 is structured with a digital communication processing unit, a modulator unit, a demodulator unit, and a line driver (analog amplifier) and the like, each of which is not shown.
As described above, when PLC modem 61 is installed in household electrical appliance 63, there is a problem that household electrical appliance 63 is associated with complication of the circuitry and an increase in costs. Accordingly, how to simplify the circuitry and suppress in an increase in the cost becomes the problem to be solved.